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Properties of voltage‐activated [Ca 2+ ] i transients in single smooth muscle cells isolated from pregnant rat uterus
Author(s) -
Shmigol A. V.,
Eisner D. A.,
Wray Susan
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.803bg.x
Subject(s) - depolarization , chemistry , membrane potential , calcium , biophysics , nifedipine , analytical chemistry (journal) , biochemistry , biology , chromatography , organic chemistry
1 The intracellular calcium concentration ([Ca 2+ ] i ) was measured at 35 °C using the fluorescent indicator indo‐1 in patch‐clamped, single uterine myocytes from pregnant rats to investigate the relationship between depolarization, Ca 2+ current ( I Ca ) and [Ca 2+ ] i . 2 Membrane depolarization activated I Ca and produced a [Ca 2+ ] i transient. The rapid increase in [Ca 2+ ] i occurred at the same time as the inward I Ca . Both I Ca and the increase in [Ca 2+ ] i were abolished by nifedipine (10 μ m ). 3 When the membrane potential was held at ‐80 mV the threshold depolarization for an increase in [Ca 2+ ] i was about ‐55 to ‐50 mV. As the magnitude of the depolarization was increased to about 0 mV there was an increase in the size of both I Ca and the increase in [Ca 2+ ] i . As the magnitude of the depolarization was further increased both I Ca and the [Ca 2+ ] i increase declined. 4 When the depolarizing pulses were applied at 3 Hz to mimic normal action potentials then the individual [Ca 2+ ] i transients did not fully relax and a tetanic rise of [Ca 2+ ] i was observed. Under these conditions, there was not a simple relationship between the magnitude of the Ca 2+ response and Ca 2+ entry. When pairs of depolarizing pulses were applied, the increase in [Ca 2+ ] i produced by the second pulse was larger (in relation to the magnitude of the L‐type Ca 2+ current) than that produced by the first pulse. This facilitation was abolished by both ryanodine and cyclopiazonic acid suggesting a role for release from intracellular stores. 5 We conclude that the L‐type Ca 2+ current is the major source of Ca 2+ ions entering the cell to produce the [Ca 2+ ] i transient on depolarization. The magnitude of the increase in [Ca 2+ ] i may, however, be amplified by Ca 2+ ‐induced Ca 2+ release.