T‐channel‐like pharmacological properties of highvoltage‐activated, nifedipine‐insensitive Ca²⁺ currents inthe rat terminal mesenteric artery

Abstract

1 Pharmacological properties of nifedipine-insensitive, high voltage-activated Ca 2+ channels in rat mesenteric terminal arteries (NICCs) were investigated and compared with those of a1E and a1G heterologously expressed in BHK and HEK293 cells respectively, using the patch clamp technique. 2 With 10 mM Ba 2+ as the charge carrier, rat NICCs (unitary conductance: 11.5 pS with 110 mM Ba 2+ ) are almost identical to those previously identi®ed in a similar region of guinea-pig, such as in current-voltage relationship, voltage dependence of activation and inactivation, and divalent cation permeability. However, these properties are considerably dierent when compared with a1E and a1G. 3 SNX-482(200 nM and sFTX3.3 (1 mM), in addition to o-conotoxin GVIA (1 mM) and o-agatoxin IVA (100 nM), were totally ineective for rat NICC currents, but signi®cantly suppressed a1E (by 82% at 200 nM; IC 50 =11.1 nM) and a1G (by 20% at 1 mM) channel currents, respectively. A nonspeci®c T-type Ca 2+ channel blocker nimodipine (10 mM) dierentially suppressed these three currents (by 40, 3 and 85% for rat NICC, a1E and a1G currents, respectively). 4 Mibefradil, the widely used T-type channel blocker, almost equally inhibited rat NICC and a1G currents in a voltage-dependent fashion with similar IC 50 values (3.5 and 0.3 mM and 2.4 and 0.14 mM at 7100 and 760 mV, respectively). Furthermore, other organic T-type channel blockers such as phenytoin, ethosuximide, an arylpiperidine derivative SUN N5030 (IC 50 =0.32 mM at 760 mV for a1G) also exhibited comparable inhibitory ecacies for NICC currents (inhibited by 22% at 100 mM; IC 50 =27.8 mM; IC 50 =0.53 mM, respectively). 5 These results suggest that despite distinctive biophysical properties, the rat NICCs have indistinguishable pharmacological sensitivities to many organic blockers compared with T-type Ca 2+ channels.

Protein kinase a regulation of T-type Ca2+ channels in rat cerebral arterial smooth muscle

“…Over a comparable time frame, control experiments revealed no significant changes in T-type current amplitude ( Fig. 6A), an observation similar to earlier reports that T-type currents are rundown-resistant in isolated vascular smooth muscle (Wang et al, 1989;Morita et al, 2002). Indirect PKA modulation through the upstream activation of adenylyl cyclase and subsequent accumulation of endogenous cAMP (1 mM forskolin; Fig.…”

“…In studies of vascular smooth muscle, investigators have typically employed dihydropyridines to separate among T-and L-type currents (Morita et al, 2002;Nikitina et al, 2007;Kuo et al, 2010;El-Rahman et al, 2013;Smirnov et al, 2013). Nifedipine is the agent of choice as it blocks the smooth muscle variant of the L-type channels (IC 50 ,10 nM) at concentrations that do not interfere with T-type activity (Akaike et al, 1989;Liao et al, 2007).…”

Depolarization‐induced calcium influx in rat mesenteric small arterioles is mediated exclusively via mibefradil‐sensitive calcium channels

“…Mibefradil has been shown to block T-type channels with an IC 50 of 100À300 nM (Mishra & Hermsmeyer, 1994;Martin et al, 2000;Hansen et al, 2001;Morita et al, 2002). In rat mesenteric small arterioles, mibefradil was indeed effective at all the concentrations tested when a special protocol designed for use-dependent drugs was applied (Figures 5a and b).…”

“…Recent studies show use-or voltage-dependent block by mibefradil for both high-and low-voltage-activated Ca 2 þ channels (Bezprozvanny & Tsien, 1995;Arnoult et al, 1998;McDonough & Bean, 1998;Jimenez et al, 2000;Morita et al, 2002). We designed a stimulation protocol to be able to show use dependence of mibefradil.…”

Dual Signaling Pathways of Arterial Constriction by Extracellular Uridine 5′-Triphosphate in the Rat

“…For the current clamp recording, the internal solution was changed to the following: 140 mM KCl, 1.5 mM MgCl 2 , 10 mM HEPES, 10 mM glucose, and 1 mM EGTA (pH = 7.4, Tris). Chemicals were applied by the 'Y-tube' fast solution change device described of Morita et al (14). Modified Krebs solution, warmed to 37°C for tension recording, contained 121.9 mM NaCl, 4.7 mM KCl, 1.2 mM MgCl 2 , 2.5 mM CaCl 2 , 15.5 mM NaHCO 3 , 1.2 mM KH 2 PO 4 , and 11.5 mM glucose (pH = 7.4) continuously aerated with 97% O 2 and 3% CO 2 .…”