Fujii T, Tokutomi N, Hirata A, Negi A, Nishi K
Department of Ophthalmology, Kumamoto University School of Medicine, Japan.
Curr Eye Res. 1997 May;16(5):436-44. doi: 10.1076/ceyr.16.5.436.7043.
The dependence of plasmalemma Ca2+ influx and Ca2+ release from intracellular stores on Ca2+ activated K+ channels of bovine ciliary muscle (CM) cells were examined.
The nystatin-perforated patch clamp technique for the measurement of membrane currents and a microscope based fura-2 fluorescence imaging of [Ca2+]i were applied to CM cells freshly dissociated with collagenase and identified with smooth muscle-specific alpha-isoactin.
At holding voltages (VH) of > -60 mV, CM cells showed spontaneous transient outward currents (STOCs) and caffeine (> 10(-4) M) induced large transient outward currents (ICAF). Both STOCs and ICAF were abolished by tetraethylammonium chloride (10(-3) M) and charybdotoxin (10(-7) M), but not by apamin (10(-6) M), suggesting that both currents are mediated by Ca(2+)-activated K+ channels similar to those with medium (MK) or large (BK-type) conductance. Both STOCs and ICAF were gradually abolished in the nominally Ca(2+)-free and Co(2+)-containing solutions but were resistant to L-type Ca2+ channel blockers, including nicardipine, verapamil and diltiazem and a N-type channel blocker, omega-contoxin. The [Ca2+]i-elevation during high K+ (100 mM)-depolarization was prevented by Ca(2+)-free and Co(2+)-containing solutions but not by nicardipine.
These results suggest that CM cells possess MK or BK type-like Ca(2+)-activated K+ channels and that L-type Ca2+ channels play minor roles for the maintenance of Ca(2+)-dependent responses in contrast to other types of smooth muscle cells.
研究牛睫状肌（CM）细胞的质膜Ca2+内流以及细胞内钙库释放Ca2+对Ca2+激活的K+通道的依赖性。
采用制霉菌素穿孔膜片钳技术测量膜电流，并运用基于显微镜的fura-2荧光成像技术检测[Ca2+]i，对用胶原酶新鲜解离并用平滑肌特异性α-异肌动蛋白鉴定的CM细胞进行研究。
在保持电压（VH）＞-60 mV时，CM细胞表现出自发性瞬时外向电流（STOCs），咖啡因（＞10-4 M）可诱导出大的瞬时外向电流（ICAF）。四乙铵（10-3 M）和蝎毒素（10-7 M）可消除STOCs和ICAF，但蜂毒明肽（10-6 M）不能，这表明这两种电流均由与中等电导（MK）或大电导（BK型）通道相似的Ca2+激活的K+通道介导。在无钙和含钴的溶液中，STOCs和ICAF均逐渐消失，但对包括尼卡地平、维拉帕米和地尔硫䓬在内的L型钙通道阻滞剂以及N型通道阻滞剂ω-芋螺毒素具有抗性。无钙和含钴的溶液可阻止高钾（100 mM）去极化期间的[Ca2+]i升高，但尼卡地平不能。
这些结果表明，CM细胞具有MK或BK型样Ca2+激活的K+通道，与其他类型的平滑肌细胞相比，L型钙通道在维持Ca2+依赖性反应中起次要作用。
