, Volume 28, Issue 1, pp 31-44

Longitudinal smooth muscle of the mammalian intestine

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Ca2+ mobilization in muscle cells from the circular muscle layer of the mammalian intestine is mediated by IP3-dependent Ca2+ release. Ca2+ mobilization in muscle from the adjacent longitudinal muscle layer involves a distinct, phosphoinositide-independent pathway. Receptors for contractile agonists in longitudinal muscle cells are coupled via a pertussis toxinsensitive G protein to activation of PLA2 and formation of arachidonic acid (AA). The latter activates Cl channels resulting in depolarization of the plasma membrane and opening of voltage-sensitive Ca2+ channels. Ca2+ influx via these channels induces Ca2+ release by activating sarcoplasmic ryanodine receptor/Ca2+ channels. The increase in [Ca2+]i activates membrane-bound ADP ribosyl cyclase, and the resultant formation of cADPR enhances Ca2+-induced Ca2+ release.