Ca2+ images and K+ current during depolarization in smooth muscle cells of the guinea-pig vas deferens and urinary bladder

• Published in: The Journal of physiology Vol. 510; no. 3; pp. 705 - 719
• Main Authors: Imaizumi, Yuji, Torii, Yuichi, Ohi, Yoshiaki, Nagano, Norihiro, Atsuki, Kaoru, Yamamura, Hisao, Muraki, Katsuhiko, Watanabe, Minoru, Bolton, Thomas B.
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 01.08.1998; Blackwell Science Ltd; Blackwell Science Inc
• Subjects: Action Potentials - drug effects; Aniline Compounds; Animals; Calcium - metabolism; Calcium Channel Blockers - pharmacology; Cell Membrane - drug effects; Cell Membrane - metabolism; Electric Stimulation; Electrophysiology; Fluorescent Dyes; Guinea Pigs; Image Processing, Computer-Assisted; In Vitro Techniques; Male; Membrane Potentials - drug effects; Membrane Potentials - physiology; Muscle, Smooth - cytology; Muscle, Smooth - drug effects; Muscle, Smooth - metabolism; Original; Patch-Clamp Techniques; Potassium Channel Blockers; Potassium Channels - agonists; Potassium Channels - metabolism; Urinary Bladder - cytology; Urinary Bladder - drug effects; Urinary Bladder - metabolism; Vas Deferens - cytology; Vas Deferens - drug effects; Vas Deferens - metabolism; Xanthenes
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.1998.705bj.x

Electrical events and intracellular calcium concentration ([Ca 2+ ]) imaged using fluo-3 and laser scanning confocal microscopy were simultaneously monitored in single smooth muscle cells freshly isolated from guinea-pig vas deferens or urinary bladder. Images obtained every 8 ms, during stepping from -60 to 0 or +10 mV for 50 ms under voltage clamp, showed that a rise in [Ca 2+ ] could be detected within 20 ms of depolarization in five to twenty small (< 2 μm diameter) ‘hot spots’, over 95 % of which were located within 1.5 μm of the cell membrane. Depolarization at 30 s intervals activated hot spots at the same places. Cd 2+ or verapamil abolished both hot spots and Ca 2+ -activated K + current ( I K,Ca ). Caffeine almost abolished hot spots and markedly reduced I K,Ca . Cyclopiazonic acid, which raised basal global [Ca 2+ ], decreased the rise in hot spot [Ca 2+ ] and I K,Ca amplitude during depolarization. These results suggest that Ca 2+ entry caused Ca 2+ -induced Ca 2+ release (CICR). Under voltage clamp, hot spot [Ca 2+ ] closely paralleled the rise in I K,Ca and reached a peak within 20 ms of the start of depolarization, but the rise in global [Ca 2+ ] over the whole cell area was much slower. Step depolarization to potentials positive to -20 mV caused hot spots to grow in size and coalesce, leading to a rise in global [Ca 2+ ] and contraction. Ca 2+ hot spots also occurred during the up-stroke of an evoked action potential under current clamp. It is concluded that the entry of Ca 2+ in the early stages of an action potential evokes CICR from discrete subplasmalemma Ca 2+ storage sites and generates hot spots that spread to initiate a contraction. The activation of Ca 2+ -dependent K + channels in the plasmalemma over hot spots initiates I K,Ca and action potential repolarization.