The effect of high [K(+)]o on spontaneous Ca(2+) waves in freshly isolated interstitial cells of Cajal from the rabbit urethra.
Physiol Rep 2014;
2:e00203. [PMID:
24744882 PMCID:
PMC3967686 DOI:
10.1002/phy2.203]
[Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2013] [Revised: 12/19/2013] [Accepted: 12/23/2013] [Indexed: 11/20/2022] Open
Abstract
Interstitial cells of Cajal (ICC) act as putative pacemaker cells in the rabbit urethra. Pacemaker activity in ICC results from spontaneous global Ca2+ waves that can be increased in frequency by raising external [K+]. The purpose of this study was to elucidate the mechanism of this response. Intracellular [Ca2+] was measured in fluo‐4‐loaded smooth muscle cells (SMCs) and ICC using a Nipkow spinning disk confocal microscope. Increasing [K+]o to 60 mmol/L caused an increase in [Ca2+]i accompanied by contraction in SMCs. Raising [K+]o did not cause contraction in ICC, but the frequency of firing of spontaneous calcium waves increased. Reducing [Ca2+]o to 0 mmol/L abolished the response in both cell types. Nifedipine of 1 μmol/L blocked the response of SMC to high [K+]o, but did not affect the increase in firing in ICC. This latter effect was blocked by 30 μmol/L NiCl2 but not by the T‐type Ca2+ channel blocker mibefradil (300 nmol/L). However, inhibition of Ca2+ influx via reverse‐mode sodium/calcium exchange (NCX) using either 1 μmol/L SEA0400 or 5 μmol/L KB‐R7943 did block the effect of high [K+]o on ICC. These data suggest that high K+ solution increases the frequency of calcium waves in ICC by increasing Ca2+ influx through reverse‐mode NCX.
Pacemaker activity in ICC results from spontaneous global Ca2+ waves that can be increased in frequency by raising external [K+]. The experiments described support the hypothesis that high K+ solution increases the frequency of calcium waves in ICC by increasing Ca2+ influx through reverse‐mode NCX.
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