Suppressive effects of somatostatin in dog Purkinje fibres

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Abstract
1 The effects of somatostatin (SS, 1 nm-3 μm) on the electrical and mechanical activities of isolated Purkinje fibres of the dog were studied. 2 In most Purkinje fibres driven electrically in normal [K]o Tyrode solution, SS decreased the force of contraction slightly and had very little effect on the fast response action potential. However, in sensitive fibres SS induced a moderate reduction of action potential duration and contractile force in normal [K]o and depressed the slow response action potentials in high [K]o. 3 In spontaneously beating Purkinje fibres, SS decreased the regular rhythms slightly but abolished bursts of fast rhythms at a concentration as low as 1 nm. 4 When the fibres were depolarized in the presence of 0.2 mm barium or in Na-free solution, SS suppressed the Ca-dependent slow response action potentials. 5 These findings suggest that SS may suppress abnormal automatic activity of dog Purkinje fibres through a reduction of transmembrane Ca influx or a modulation of intracellular calcium.