Inositol 1,4,5-Trisphosphate-Induced Ca^<2+>-Transient and Outward K^+ Current in Single Smooth Muscle Cells of Guinea Pig Small Intestine

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    • ITO Shigeo
    • Department of Pharmacology and Clinical Pharmacology, St. George's Hospital Medical School
    • BOLTON Thomas B.
    • Department of Pharmacology and Clinical Pharmacology, St. George's Hospital Medical School


The effects of inositol 1, 4, 5-trisphosphate (InsP<SUB>3</SUB>) released from caged InsP<SUB>3</SUB> by flash photolysis on free intracellular Ca<SUP>2+</SUP> concentration, [Ca<SUP>2+</SUP>]<SUB>i</SUB>, and outward K<SUP>+</SUP> current were simultaneously examined in a single smooth muscle cell of guinea pig small intestine using a patch pipette solution containing Indo-1 (0.1 mM), caged InsP<SUB>3</SUB> (50 μM) and KCl (130 mM). At a holding potential of −50 mV, a depolarizing pulse to + 10 mV for 200 msec caused a transient Ca<SUP>2+</SUP> current and an increase in [Ca<SUP>2+</SUP>]<SUB>i</SUB>. The amplitude of the Ca<SUP>2+</SUP>-transient was positively correlated with the peak Ca<SUP>2+</SUP> current and negatively correlated with resting [Ca<SUP>2+</SUP>]<SUB>i</SUB>. InsP<SUB>3</SUB> produced increases in [Ca<SUP>2+</SUP>]<SUB>i</SUB> and outward K<SUP>+</SUP> current in most of the cells at −50 and −30 mV. The outward K<SUP>+</SUP> current response reached a peak sooner and decayed more quickly than the Indo-1 signal. Both responses to InsP<SUB>3</SUB> were resistant to the removal of extracellular Ca<SUP>2+</SUP>. The Ca<SUP>2+</SUP>-transient and outward K<SUP>+</SUP> current responses to InsP<SUB>3</SUB> at −30 mV were larger than those at −50 mV. The InsP<SUB>3</SUB>-induced Ca<SUP>2+</SUP>-transient was increased by increasing resting [Ca<SUP>2+</SUP>]<SUB>i</SUB> at −30 mV but not at −50 mV. These results suggest that InsP<SUB>3</SUB>-induced Ca<SUP>2+</SUP> release from stores is potentiated by slight increases in [Ca<SUP>2+</SUP>]<SUB>i</SUB> via membrane depolarization.


  • The Japanese Journal of Pharmacology

    The Japanese Journal of Pharmacology 71(1), 1-10, 1996-05

    The Japanese Pharmacological Society

References:  20


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