Regulation of Ca2+ channels by cAMP and cGMP in vascular smooth muscle cells.
Whole-cell Ca2+ channel currents in rabbit portal vein cells were recorded using the amphotericin B-perforated patch-clamp technique at 35 degrees C. This technique allowed recording of stable inward currents in the absence of run-down for more than 30 minutes. Depolarizing voltage steps from a holding potential of -70 mV elicited voltage-dependent inward currents. The voltage dependence of inward currents measured in either 2.5 mmol/L Ba(2+)- or 2.5 mmol/L Ca(2+)-containing solution were very similar. However, maximum Ba2+ current (obtained at around +10 mV) was approximately 1.5-fold larger than maximum Ca2+ current. Changing the holding potential from -70 to -40 mV decreased inward currents but did not shift the voltage dependence significantly. Inward currents were also completely blocked by the dihydropyridine Ca2+ channel blocker, nicardipine (10 mumol/L), suggesting the presence of predominantly L-type Ca2+ channels in rabbit portal vein cells. Isoproterenol caused small increases in the amplitude of Ba2+ currents in a concentration-dependent manner (10 nmol/L to 1 mumol/L), which were reversed with propranolol. Forskolin (1 mumol/L) or 8-bromo-cAMP (0.1 mmol/L) also caused small increases in the amplitude of Ba2+ currents, suggesting that the stimulatory actions of isoproterenol are importantly linked to the production of cAMP. Higher concentrations of of isoproterenol (10 mumol/L) or forskolin (10 mumol/L) caused a transient increase in Ba2+ currents followed by f decrease in current amplitude. Higher doses of 8-bromo-cAMP (1 mmol/L) and low doses of 8-bromo-cGMP (0.1 mmol/L) inhibited Ba2+ currents, increased the rate of current inactivation, and produced a negative voltage shift in steady-state availability. These results indicate that low concentrations of intracellular cAMP produce modest increases in Ca2+ channel activity, whereas cGMP and higher concentrations of cAMP result in inhibition of Ca2+ channel activity in vascular smooth muscle cells. The observed similarities of cGMP and high concentrations of cAMP on Ba2+ current amplitude, kinetics, and steady-state inactivation suggest mediation by a common mechanism, possibly involving activation of cGMP-dependent protein kinase.
Ishikawa
T
T
Department of Physiology, University of Nevada School of Medicine, Reno 89557-0046.
Hume
J R
JR
Keef
K D
KD
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D006152:Cyclic GMP / Q000502:physiology*; D004594:Electrophysiology; D007545:Isoproterenol / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D009712:Nucleotides, Cyclic / Q000494:pharmacology; D009994:Osmolar Concentration; D011817:Rabbits
D015220:Calcium Channels; D009712:Nucleotides, Cyclic; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000242:Cyclic AMP; D006152:Cyclic GMP; D007545:Isoproterenol