Influence of the lonic Environment on Spontaneous Electrical and Mechanical Activity of the Rat Portal Vein

Abstract

The effects of variations in external K + and Ca 2+ concentrations on electrical and mechanical activity of the isolated rat portal vein were studied using a sucrose-gap technique. Spontaneous activity in normal Krebs solution consists of bursts of action potentials accompanied by phasic contractions. • Information about the electrophysiological properties of vascular smooth muscle and the relationship between electrical and mechanical activity will provide a basis for better understanding of the action of drugs on blood vessels. This paper mainly describes results obtained by simultaneous recordings of electrical and mechanical activity of the rat portal vein. This vessel was introduced as a suitable preparation for studying electrical activity of vascular smooth muscle by Funaki and Bohr (1) working with intracellular microelectrodes. A sucrose-gap technique has been used for recording electrical activity in the present investigation. The effects of changes in the external ionic environment on membrane potential, frequency and pattern of spike discharge, and tension development, and on the normal correlation of these parameters have been studied. Another paper deals more specifically with the actions of drugs.Results pertaining to the current study have been presented in preliminary form (2, 3).

Effects of Diltiazem on Guinea Pig Portal Vein in Hypertonic Solution

“…It has been reported that the automaticity and propagation of excitation in the guinea pig portal vein are not affected by tetrodotoxin (9). In the rat portal vein, Ca` is assumed to be essential for activation of the contractile mechanism and for maintenance of the spontaneous spike discharge in isotonic solution (21).…”

Comparison of effects of a new dihydropyridine, Bay K 8644, and nifedipine on spontaneous mechanical activity in rat portal vein

“…Previous studies have shown that the contractile activity in the spontaneously active smooth muscle of the rat portal vein is highly dependent on the extracellular Ca-concentration and that Ca-antagonistic drugs, including nifedipine, have an inhibitory effect on the spontaneous mechanical activity in these vessels (Axelsson et al, 1967;Pegram & Ljung 1981;van Neuten & Vanhoutte, 1981;Mikkelsen et al, 1984).…”

Evidence for the involvement of the cyclooxygenase-metabolic pathway in diclofenac-induced inhibition of spontaneous contraction of rat portal vein smooth muscle cells

“…Since diclofenac decreased both the amplitudes of the spontaneous phasic contractions and the phasic increases in the intensities of the Fura PE3 F340/F380 ratio in a similar manner, it would appear that the diclofenac-induced inhibition of the spontaneous contractions was mediated by a decrease in the intracellular Ca 2+ concentrations. It has been shown that spontaneous contractions of the rat portal vein are accompanied by bursts of action potentials (Funaki and Bohr, 1964;Axelsson et al, 1967;Johansson et al, 1967). Both contraction and action potentials are dependent on an influx of extracellular calcium through L-type Ca 2+ channels (Sutter, 1990;Kamishima and McCarron, 1996).…”

“…Longitudinal preparations of the rat portal vein develop spontaneous phasic myogenic contractions which are accompanied by bursts of action potentials (Funaki and Bohr, 1964;Axelsson et al, 1967;Johansson et al, 1967). Because such contractions are very sensitive to extracellular calcium, the rat portal vein has been used to examine the effects of drugs on vascular contraction (Sutter, 1990).…”