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

Abstract

The electrophysiological and pharmacological properties of Ca²⁺ current (I_Ca) 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 I_Ca 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 V_test 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 µM), an L-type Ca²⁺ channels antagonist, completely inhibited I_Ca, while the L-type Ca²⁺ channels agonist Bay-K 8644 (1 µM) significantly increased I_Ca amplitude. Moreover, the selective blocker of P-/Q-type Ca²⁺ channels ω-agatoxin IVA partially blocked I_Ca (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 I_Ca registered using low extracellular Ca²⁺. The presence of the P-/Q-type Ca²⁺ channels was confirmed by immunoblot analysis. When I_Ca was recorded in a high concentration (30 mM) of extracellular Ca²⁺ or Ba²⁺ 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 µM). 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.

High K+-induced contraction requires depolarization-induced Ca2+ release from internal stores in rat gut smooth muscle

“…The involvement of additional Ca 2+ channel types is unlikely, as the inhibition of T-type, N-type and P/Q-type Ca 2+ channels by verapamil occurs at higher concentra tions [25,26] . Thus, even though T-type and P/Q-type, but not N-type Ca 2+ channels are expressed in smooth muscle [27,28] , the concentration used in our study probably reflects Ca 2+ influx through L-type channels in smooth muscle cells.…”

Genistein effects on Ca2+ handling in human umbilical artery: inhibition of sarcoplasmic reticulum Ca2+ release and of voltage-operated Ca2+ channels

“…HUA smooth muscle cells were obtained by a method based on the one described by Klockner (13) and later modified in our laboratory (21) in order to diminish the enzyme content in the dissociation medium (DM). Briefly, segments of HUA were cleaned of any residual connective tissue, cut in small strips and placed for 15 minutes in a DM containing (in mM): 140 NaCl, 5 KH 2 PO 4 , 5 MgCl 2 , 20 glucose, 5 HEPES, pH was adjusted to 7.4 with NaOH.…”

Functional Importance of L- and P/Q-Type Voltage-Gated Calcium Channels in Human Renal Vasculature

“…In agreement, Ca v 2.1-mediated currents have been observed in human umbilical arteries and rat preglomerular myocytes. 2,25 The biophysical properties vary between calcium currents. Compared with L-type currents, P/Q-type Ca 2ϩ currents are slower, have a Ca 2ϩ -independent rate of inactivation, and have inhibitory modulation by G proteins.…”