Effects of pH and ionic strength on the potassium system in the internally perfused giant barnacle muscle fibre

The effect of hypoxia on mechanical and electrical properties of smooth muscle from the rat portal vein

The effect of hypoxia on the electrical and mechanical activity of rat portal vein smooth muscle were investigated using intracellular microelectrode technique in combination with contraction force measurements. In control conditions the "resting" potential of the muscle cells was -58.0 +/- 0.1 mV (mean +/- S.E.). Bursts of action potentials, 5-10s long, appeared at regular intervals (2-3/min) in association with phasic contractions. In hypoxia (PO2 at about 10 mm Hg) there was a marked decrease in force and, often, a moderate increase in rate of the spontaneous contractions. Electrically, these changes corresponded to a decrease in length and an increase in frequency of the bursts of action potentials. The general level of membrane polarization and individual action potentials were not affected. In prolonged hypoxia there was a tendency towards dissociation of the electrical and mechanical activities. Increasing [K+]0 or reducing [Na+]0 produced a restoration of the hypoxically depressed force development. Qualitatively similar results with respect to the depression of myogenic activity by hypoxia, and its alleviation in decreased [K+]0 and reduced [Na+]0, were obtained in low Ca (1 mM) solutions. The effects of hypoxia, and their variation with [K+]0 and [Na+]0, could be explained on the basis of pH dependent electro-mechanical uncoupling.

Some electrical properties of the membrane of the barnacle muscle fibers under internal perfusion

Intracellular perfusion technique has been applied to the muscle fibers of the barnacle species, Balanus nubilus. In these fibers, generation and the form of the calcium spike was governed by the frequency of stimulation and intra- and extracellular calcium concentrations. Voltage-clamp experiments showed that the magnitude of the potassium outward current was controlled by the intracellular calcium concentration whose increase, nearly 10(3)-fold, raised the resting membrane conductance and the outward potassium current. On the other hand, application of 10 mM zinc ions inside the muscle fiber had no effect on either the resting potential or the outward potassium current but suppressed the early inward calcium current. Similarly, the inward calcium current was decreased by low concentration of sodium ions in the extracellular fluid only when its ionic strength was made low by substituting sucrose for the sodium salt. Measurement of outward current with the muscle fiber in calcium-free ASW solution and intracellularly perfused with several cationic solutions established the selectivity sequence TEA less than Cs less than Li less than Tris less than Rb less than Na less than K for the potassium channel.