L, P-/Q- and T-type Ca2+ Channels in Smooth Muscle Cells from Human Umbilical Artery

SILVIA SALEMME; ALEJANDRO REBOLLEDO; FRANCISCO SPERONI; SILVANA PETRUCCELLI; VERONICA MILESI

Cellular Physiology and Biochemistry

Karger

Lugar: Baltimore; Año: 2007 vol. 20 p. 55 - 64

1421-9778

The electrophysiological and pharmacological properties of Ca2+ current (ICa) were determined by the whole-cell configuration of the patch-clamp technique in smooth muscle cells from human umbilical artery. Using 5 mM extracellular Ca2+, depolarizing step pulses from -60 to 50 mV from a holding membrane potential of -80 mV evoked an ICa which activated at membrane potentials more positive than -50 mV and exhibited a maximum current density in a range of 10-20 mV. Steady-state inactivation protocols using a Vtest of 10 mV gave a voltage at one-half inactivation and a slope factor of -35.6 mV and 9.5 mV, respectively. Nifedipine (1 ?M), an L-type Ca2+ channels antagonist, completely inhibited ICa, while the L-type Ca2+ channels agonist Bay-K 8644 (1 ?M) significantly increased ICa amplitude. Moreover, the selective blocker of P-/Q-type Ca2+ channels ?-agatoxin IVA partially blocked ICa (about 40 % inhibition at +20 mV by 20 nM). These pharmacological results suggest that L- and P-/Q-type Ca2+ channels, both nifedipine-sensitive, underlie the ICa registered using low extracellular Ca2+. The presence of the P-/Q-type Ca2+ channels was confirmed by immunoblot analysis. When ICa was recorded in a high concentration (30 mM) of extracellular Ca2+ or Ba 2+ as current carrier, it was evident the presence of a nifedipine-insensitive component which completely inactivated during the course of the voltage-step (75 ms) at all potentials tested, and was blocked by the T-type Ca2+ channels blocker mibefradil (10 ?M). Summarizing, this work shows for the first time the electrophysiological and pharmacological properties of voltage-activated Ca2+ currents in human umbilical artery smooth muscle cells.