Voltage gated calcium channels (VGCCs) are multi-subunit membrane proteins present in a variety of tissues and control many essential physiological processes. Due to their vital importance, VGCCs are regulated by a myriad of proteins and signaling pathways. Here we review the literature on the regulation of VGCCs by proteolysis of the pore-forming α1 subunit, Ca(v)α(1). This form of regulation modulates channel function and degradation and affects cellular gene expression and excitability. L-type Ca(2+) channels are proteolyzed in two ways, depending on tissue localization. In the heart and skeletal muscle, the distal C-terminus of Ca(v)α(1) is cleaved and acts as an autoinhibitor when it reassociates with the proximal C-terminus. Relief of this autoinhibition underlies the β-adrenergic stimulation-induced enhancement of cardiac and skeletal muscle calcium currents, part of the "fight or flight" response. Proteolysis of the distal C-terminus of L-type channels also occurs in the brain and is probably catalyzed by a calpain-like protease. In some brain regions, the entire C-terminus of L-type Ca(2+) channels can be cleaved by an unknown protease and translocates to the nucleus acting as a transcription factor. The distal C-terminus of P/Q-channel Ca(v)α(1) is also proteolyzed and translocates to the nucleus. Truncated forms of the PQ-channel Ca(v)α(1) are produced by many disease-causing mutations and interfere with the function of full-length channels. Truncated forms of N-type channel Ca(v)α(1), generated by mutagenesis, affect the expression of full-length channels. New forms of proteolysis of VGCC subunits remain to be discovered and may represent a fruitful area of VGCC research.
Animals ; Calcium Channels, L-Type ; metabolism ; Calcium Signaling ; Humans ; Muscle, Skeletal ; physiology ; Proteolysis

OBJECTIVETo explore the mechanisms of the influx of calcium ions during the activation of ACh-sensitive BK channel (big conductance, calcium-dependent potassium channel) in type II vestibular hair cells of guinea pigs.

METHODSType II vestibular hair cells were isolated by collagenase type IA. Under the whole-cell patch mode, the sensitivity of ACh-sensitive BK current to the calcium channels blockers was investigated, the pharmacological property of L-type calcium channel activator-sensitive current and ACh-sensitive BK current was compared.

RESULTSFollowing application of ACh, type II vestibular hair cells displayed a sustained outward potassium current, with a reversal potential of (-70.5 +/- 10.6) mV (x +/- s, n = 10). At the holding potential of -50 mV, the current amplitude of ACh-sensitive potassium current activated by 100 micromol/L ACh was (267 +/- 106) pA (n = 11). ACh-sensitive potassium current was potently sensitive to the BK current blocker, IBTX (iberiotoxin, 200 nmol/L). Apamin, the well-known small conductance, calcium-dependent potassium current blocker, failed to inhibit the amplitude of ACh-sensitive potassium current at a dose of 1 micromol/L. ACh-sensitive BK current was sensitive to NiCl2 and potently inhibited by CdCl2. NiCl2 and CdCl2 showed a dose-dependent blocking effect with a half inhibition-maximal response of (135.5 +/- 18.5) micromol/L (n = 7) and (23.4 +/- 2.6) micromol/L (n = 7). The L-type calcium channel activator, (-) -Bay-K 8644 (10 micromol /L), mimicked the role of ACh and activated the IBTX-sensitive outward current.

CONCLUSIONACh-sensitive BK and L-type calcium channels are co-located in type II vestibular hair cells of guinea pigs.

Animals ; Calcium Channels, L-Type ; Guinea Pigs ; Hair Cells, Vestibular ; metabolism ; Large-Conductance Calcium-Activated Potassium Channels ; Patch-Clamp Techniques

Animals ; Calcium ; metabolism ; Calcium Channels, L-Type ; metabolism ; Drugs, Chinese Herbal ; pharmacology ; Hepatocytes ; metabolism ; Proteins ; metabolism ; Rats ; Rats, Sprague-Dawley

OBJECTIVETo construct a rat model of chronic nonbacterial prostatitis (CP) and investigate the difference in the quantitative expression of voltage-dependent calcium channels of prostate smooth muscle cells (PSMCs) between the models and controls.

METHODSWe established a CP rat model by estrogen induction, cultured and purified the PSMCs in vitro, and extracted total RNA by Trizol. Then we measured the mRNA expression of the cal subunit in the calcium channel subtypes by reverse transcription and SYBR Green I real time RT-PCR, and compared it with that of the controls.

RESULTSThe expressions of the L-, T- and P/Q-type calcium channels were found in both the CP and control groups, and that of the CaV1.2 L-type calcium channel was significantly increased in the former as compared with the latter (0.048 +/- 0.024 versus 0.031 +/- 0.015, t = 2.846, P = 0.007), but there were no statistically significant differences in the T- and P/Q-type calcium channels between the two groups.

CONCLUSIONThe number of CaV1.2 L-type calcium channels of PSMCs and calcium influx were increased in CP patients, which may be involved in the mechanism of CP.

Animals ; Calcium Channels, L-Type ; metabolism ; Calcium Channels, Q-Type ; metabolism ; Calcium Channels, T-Type ; metabolism ; Estradiol ; pharmacology ; Male ; Myocytes, Smooth Muscle ; metabolism ; Prostate ; metabolism ; Prostatitis ; metabolism ; RNA, Messenger ; genetics ; Rats ; Rats, Wistar

OBJECTIVETo study the expressions of L-type calcium channel alpha1c and potassium channel Kv4.3 at early stages of atrial fibrillation in a rapid paced primary cultured atrial myocyte model.

METHODSPrimary rat atrial myocytes were cultured and a rapid paced cell model was established. The atrial cells were divided into five groups with pacing durations within 0 and 24 h. Reverse transcription-polymerase chain reaction and Western blot were applied to detect the messenger ribonucleic acid (mRNA) and proteins of L-type calcium channel alpha1c and potassium channel Kv4.3, respectively.

RESULTSmRNA expression of L-type calcium channel alpha1c reduced after 6 h of rapid pacing and continued to decline as the pacing process. The decrease of L-type calcium channel alpha1c protein was paralleled with mRNA expression and reached the lowest levels at 24 h. Similarly, changes of potassium channel Kv4.3 protein and mRNA were paralleled. Kv4.3 mRNA was not altered within the first 6 h. It was reduced after 12 h. However, longer pacing periods did not further decrease mRNA and protein expression levels of potassium channel Kv4.3.

CONCLUSIONSExpressions of L-type calcium channel alpha1c and potassium channel Kv4.3 were both reduced at different levels in early phase of rapid pacing atrial myocytes. It implicates the occurrence of ion channel remodeling of atrial myocytes, which may serve as molecular mechanism of electrical remodeling in the development of atrial fibrillation.

Animals ; Atrial Fibrillation ; metabolism ; physiopathology ; Calcium Channels, L-Type ; metabolism ; Cardiac Pacing, Artificial ; Cells, Cultured ; Myocytes, Cardiac ; metabolism ; RNA, Messenger ; metabolism ; Rats ; Rats, Wistar ; Shal Potassium Channels ; metabolism

The aim of this study was to investigate the effect of interleukin 6 (IL-6) on the contraction of colon longitudinal muscle strips in rats with acute pancreatitis (AP) and its underlying mechanism. Rat AP model was established by combined injection (i. p.) of ceruletide and lipopolysaccharide. The effect of IL-6 on spontaneous contraction of longitudinal smooth muscle strips of rat colon was observed by biological function experiment system. The level of serum IL-6 was detected by ELISA, the expression and distribution of IL-6 in colon were observed by histochemical staining, and the effect of IL-6 on L-type calcium channel in colon smooth muscle cells was observed by whole cell patch clamp technique. The results showed that, compared with the control group, AP group exhibited reduced contractile amplitude and longer contraction cycle of colon smooth muscle strips. IL-6 prolonged the contraction cycle of colon smooth muscle strips, but did not affect their spontaneous contraction amplitude. Serum IL-6 concentration in AP group was significantly higher than that in control group (P > 0.05). IL-6 was diffusely distributed in the colon of the control group, but the expression of IL-6 was significantly up-regulated in the colon gland, mucosa and submucosa of the AP group. IL-6 significantly decreased the peak current density of L-type calcium channel in rat colon smooth muscle cells. These results suggest that the colon motility of AP rats is weakened, and the mechanism may be that up-regulated IL-6 inactivates L-type voltage-dependent calcium channels, and then inhibits the contraction of colon longitudinal smooth muscle.
Animals ; Calcium Channels, L-Type ; metabolism ; Colon ; Interleukin-6 ; metabolism ; Muscle Contraction ; Muscle, Smooth ; physiopathology ; Pancreatitis ; physiopathology ; Rats

The aim of the present study is to investigate the alterations of cardiac hemodynamics, sodium current (I(Na)) and L-type calcium current (I(Ca-L)) in the cardiomyopathic model of rats. The model of cardiomyopathy was established by intraperitoneal injection of L-thyroxine (0.5 mg/kg) for 10 d. The hemodynamics was measured with biological experimental system, and then I(Na) and I(Ca-L) were recorded by using whole cell patch clamp technique. The results showed that left ventricular systolic pressure (LVSP), left ventricular developed pressure (LVDP), +/-dp/dt(max) in cardiomyopathic group were significantly lower than those in the control group, while left ventricular end-diastolic pressure (LVEDP) in cardiomyopathic group was higher than that in the control group. Intraperitoneal injection of L-thyroxine significantly increased the current density of I(Na) [(-26.2+/-3.2) pA/pF vs (-21.1+/-6.3) pA/pF, P<0.01], shifted steady-state activation and inactivation curves negatively, and markedly prolonged the time constant of recovery from inactivation. On the other hand, the injection of L-thyroxine significantly increased the current density of I(Ca-L) [(-7.9+/-0.8) pA/pF vs (-5.4+/-0.6) pA/pF, P<0.01)], shifted steady-state activation and inactivation curves negatively, and obviously shortened the time constant of recovery from inactivation. In conclusion, the cardiac performance of cardiomyopathic rats is similar to that of rats with heart failure, in which the current density of I(Na) and especially the I(Ca-L) are enhanced, suggesting that calcium channel blockade and a decrease in Na(+) permeability of membrane may play an important role in the treatment of cardiomyopathy.
Animals ; Calcium Channels, L-Type ; metabolism ; Cardiomyopathies ; chemically induced ; metabolism ; physiopathology ; Hemodynamics ; physiology ; Male ; Myocardium ; metabolism ; Patch-Clamp Techniques ; Rats ; Rats, Sprague-Dawley ; Sodium Channels ; metabolism ; Thyroxine

OBJECTIVETo investigate rapid atrial pacing (RAP) induced atrial ultrastructural changes and mRNA and protein expression changes of L-type calcium channel subunits and potassium channel Kv4.3 in a rabbit model.

METHODSThirty-six rabbits were electrically paced at a frequency of 600 beats/min for durations ranging from 0 - 48 h via bipolar endocardial leads through surgical techniques. Ultrastructural changes of the atrium were observed through a transmission electron microscope (TEM), L-type calcium channel subunits and potassium channel Kv4.3 expressions at mRNA and protein levels were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot.

RESULTSAtrial ultrastructure changes characterized by mitochondrial vacuolization, myofilament lysis, and glycogen accumulation were detected obvious at 3 h post pacing. Down-regulated mRNA expression of Ca(2+) channel beta1 and alpha1 subunits was observed 6 h post pacing, Kv4.3 mRNA down-regulation occurred 24 h post pacing, auxiliary subunit alpha2 was not affected by pacing. Protein expression of alpha1c subunit and potassium channel Kv4.3 paralleled their mRNA expression changes.

CONCLUSIONRAP induced ultrastructural changes of the atrium and down-regulated mRNA and protein expressions of L-type calcium channel subunits and potassium channel Kv4.3 occurred thereafter in response to intracellular calcium overload induced by RAP.

Animals ; Calcium Channels, L-Type ; genetics ; metabolism ; Cardiac Pacing, Artificial ; methods ; Female ; Heart Atria ; metabolism ; ultrastructure ; Male ; Patch-Clamp Techniques ; Potassium Channels ; genetics ; metabolism ; RNA, Messenger ; metabolism ; Rabbits

OBJECTIVETo study the expression of the L-type calcium channel (Cav1.3) and its receptor Ryrs1 in the corpus cavernosum of the penis in aged rats, and to explore the mechanism of age-related erectile dysfunction (ED).

METHODSWe included 10 two month-old male SD rats (Group A) and another ten 18-month-old ones (Group B) in this study, measured their serum testosterone levels and analyzed the expressions of Cav1.3 and RyR1 in the corpus cavernosum of the penis by RT-PCR and immunohistochemistry.

RESULTSThe level of serum testosterone was significantly lower in Group B than in A ([1 356 +/- 424] ng/L vs [2 744 +/- 964] ng/L, P < 0.05). Compared with the young rats, the aged ones showed significant decreases in the expressions of Cav1.3 (IA = 18.65 +/- 8.47 vs 75.48 +/- 14.28, P < 0.05), RyR1 (IA = 21.37 +/- 9.64 vs 78.23 +/- 13.57, P < 0.05), Cav1.3 mRNA (mean gray value = 0.382 +/- 0.046 vs 1.137 +/- 0.415, P < 0.05), and RyR1 mRNA (mean gray value = 0.146 +/- 0.053 vs 1.215 +/- 0.261, P < 0.05).

CONCLUSIONReduced expressions of Cav1.3 and RyR1 in the corpus cavernosum of the penis may be one of the mechanisms underlying age-related ED in aged rats.

Aging ; Animals ; Calcium Channels, L-Type ; metabolism ; Erectile Dysfunction ; metabolism ; Male ; Penis ; metabolism ; Rats ; Rats, Sprague-Dawley ; Ryanodine Receptor Calcium Release Channel ; metabolism

OBJECTIVETo investigate the molecular and functional changes in L-type Ca2+ channel of hypertrophied cardiomyocytes in neonatal rats induced by angiotensin II (Ang II).

METHODSThe in vitro model of cardiomyocyte hypertrophy was established in cultured cardiomyocytes from neonatal rats. Whole cell patch clamp was used to measure the L-type Ca2+ currents. Semi-quantitative RT-PCR was used to determine the mRNA expression of L-type Ca2+ channel alpha1C subunits.

RESULTSIn the hypertrophied cardiomyocytes induced by Ang II, I(Ca, L) densities were increased, whereas the features of I(Ca,L) activation, inactivation or recovery from inactivation were not affected. Meanwhile, Ang II increased the mRNA expression of L-type Ca2+ channel alpha1C subunits in cardiomyocytes. All these actions of Ang II could be blocked by the angiotensin II 1 type receptor blocker losartan.

CONCLUSIONDuring cardiomyocyte hypertrophy induced by Ang II, there are significant changes in the molecule and function of L-type Ca2+ channels, which are mediated by the angiotensin II 1 type receptor.

Angiotensin II ; adverse effects ; Animals ; Calcium ; metabolism ; Calcium Channels, L-Type ; metabolism ; Female ; Hypertrophy ; metabolism ; Male ; Membrane Potentials ; Myocytes, Cardiac ; metabolism ; pathology ; physiology ; Rats ; Rats, Sprague-Dawley