Premium
Actions of guanine nucleotides and cyclic nucleotides on calcium stores in single patch‐clamped smooth muscle cells from rabbit portal vein
Author(s) -
Komori S.,
Bolton T.B.
Publication year - 1989
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1989.tb12039.x
Subject(s) - caffeine , chemistry , gtp' , carbachol , biophysics , patch clamp , calcium , ryanodine receptor , medicine , endocrinology , n ethylmaleimide , intracellular , biochemistry , biology , receptor , enzyme , organic chemistry
1 Single smooth muscle cells were obtained from the rabbit portal vein by enzymic digestion and membrane currents under voltage clamp measured by whole‐cell patch clamp technique. 2 When held at depolarized potentials, spontaneous outward currents (STOCs) were discharged; it is likely that these represent the cyclical storage and release within the cell of calcium in relation to Ca‐activated K‐channels. 3 Application of lower concentrations of carbachol (10 −5 m ) or caffeine (10 −3 m ) accelerated STOC discharge. Higher concentrations of caffeine (10 −2 m ) or carbachol (10 −4 m ), or noradrenaline (10 −5 m ), produced an outward current of 1–5 nA which disappeared within 5–15 s and which was considered to result from the discharge of calcium stores; STOC discharge was abolished for a period. 4 Ryanodine (10 −5 ‐10 −4 m ) or a non‐hydrolysable GTP analogue, GTPγS (10 −5 ‐10 −3 m ) introduced into the cell abolished STOC discharge within 2–5 min. STOCs were large in cells filled with GDPβS (10 −3 m ) and the action of GTPγS introduced at various concentrations was antagonized. 5 GTPγS (10 −4 ‐10 −3 m ) in the cell reduced or abolished outward current to caffeine (10 −2 m ) noradrenaline (10 −5 m ) or carbachol (10 −4 m ); the effect on caffeine outward current was antagonized by GDPβS (10 −3 m ) introduced into the cell. GDPβS reduced noradrenaline outward current but not caffeine outward current implying the existence of a G‐protein step in noradrenaline‐evoked Ca‐store release, possibly regulating phospholipase C enzyme activity and D‐myo inositol 1,4,5 trisphosphate formation. 6 If cyclic AMP (10 −3 m ) or cyclic GMP (10 −3 m ) was introduced into the cell, or 8‐bromo cyclic AMP (0.5 × 10 −3 m ) or 8‐bromo cyclic GMP (0.5 × 10 −3 m ) applied to the cell in the bathing solution, STOC discharge was only slightly affected. However, the outward current to caffeine applied after noradrenaline was much enhanced. 7 The results could be explained if cyclic GMP and cyclic AMP enhance calcium storage whereas GTPγS depletes calcium stores, an action antagonized by GDPβS.