Inhibitory effects of histamine and bradykinin on calcium current in smooth muscle cells isolated from guinea‐pig ileum.

Abstract

1. Single smooth muscle cells were isolated from the longitudinal muscle layer of the guinea-pig ileum and within 10 h Ca(2+)-currents (ICa) were recorded using the whole-cell patch clamp technique. 2. Histamine (10 microMs) and bradykinin (BK, 1 microM) suppressed ICa; the effect had two phases: a rapid and transient suppression of ICa followed by a sustained suppression. Acetylcholine and substance P appeared to have similar effects but these were not investigated in detail. 3. The effects of histamine and BK on ICa were established by high intracellular concentrations of the Ca2+ buffer EGTA (30 mM) or 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) (5 mM) in the absence of Ca2+ added to the pipette solution. When [Ca2+]i was strongly buffered to 125 or 190 nM by BAPTA-Ca2+ mixtures in the pipette the transient suppression of ICa was blocked but the sustained effect still occurred. This indicated that the transient effect was caused by a rise in [Ca2+]i. The sustained effect, in contrast, did not seem to be caused by a rise in [Ca2+]i but did show Ca2+ dependence because it did not occur if [Ca2+]i was abnormally low. 4. Application of caffeine (10 mM) to deplete stored Ca2+ or intracellular heparin (1 mM) to block the action of D-myo-inositol 1,4,5-trisphosphate (IP3) to release stored Ca2+ prevented the transient but not the sustained suppression of ICa. Heparin also blocked the transient Ca(2+)-activated K+ current in response to histamine or BK. Both transient and sustained suppressions of Ca2+ channel activity were observed in the absence of extracellular Ca2+ when current was carried mostly by Na+ ions. 5. Intracellular guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S; 10 or 100 microM) induced a gradual decline of ICa upon which transient decreases of current were superimposed. Histamine caused a larger than normal inhibition of ICa and no recovery occurred on wash-out. Intracellular guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S; 1 mM) abolished the effects of histamine and BK on ICa.(ABSTRACT TRUNCATED AT 400 WORDS)