We have studied the interactions of Ba ion with K channels. Ba2+ blocks these channels when applied either internally or externally in millimolar concentrations. Periodic depolarizations enhance block with internal Ba2+, but diminish the block caused by external Ba2+. At rest, dissociation of Ba2+ from blocked channels is very slow, as ascertained by infrequent test pulses applied after washing...

We have developed an assay for the duration of membrane excitation in Paramecium tetraurelia by tracing the influx of 133Ba2+. This assay is performed at physiological temperatures and in physiological solutions. Ba2+ enters the paramecia through the Ca channels, since mutants defective in Ca channels show no significant Ba2+ influx. Ba2+ enters only when the Ca channels are opened during excit...

IKx is a voltage-dependent K+ current in the inner segment of rod photoreceptors that shows many similarities to M-current. The depression of IKx by external Ba2+ was studied with whole-cell voltage clamp. Ba2+ reduced the conductance and voltage sensitivity of IKx tail currents and shifted the voltage range over which they appeared to more positive potentials. These effects showed different se...

We examined Ba2+ influx using isotopic and fura-2 techniques in transfected Chinese hamster ovary cells expressing the bovine cardiac Na+/Ca2+ exchanger (CK1.4 cells). Ba2+ competitively inhibited exchange-mediated 45Ca2+ uptake with a Ki approximately 3 mM. Ba2+ uptake was stimulated by pretreating the cells with ouabain and by removing extracellular Na+, as expected for Na+/Ba2+ exchange acti...

Cardiac muscle fails to relax upon replacement of extracellular Ca2+ with Ba2+. Among the manifold consequences of this intervention, one major possibility is that Na(+)-Ba2+ exchange is inadequate to support normal relaxation. This could occur due to reduced transport rates of Na(+)-Ba2+ exchange and/or by failure of Ba2+ to activate the exchanger molecule at the high affinity regulatory Ca2+ ...

Ba2+ block of large conductance Ca2+-activated K+ channels was studied in patches of membrane excised from cultures of rat skeletal muscle using the patch clamp technique. Under conditions in which a blocking Ba2+ ion would dissociate to the external solution (150 mM N-methyl-D-glucamine+o, 500 mM K+i, 10 microM Ba2+i, +30 mV, and 100 microM Ca2+i to fully activate the channel), Ba2+ blocks wit...

The mechanism of the Ba2+-induced contraction was investigated using intact and saponin-treated skinned smooth muscle (skinned muscle) strips of the rabbit mesenteric artery. After depletion of Ca2+ stored in the caffeine-sensitive site, greater than 0.65 mM Ba2+ evoked contraction in muscle strips depolarized with 128 mM K+ in Ca2+-free solution in a dose-dependent fashion, and the ED50 values...

We have studied potassium currents through a cloned Ca(2+)-dependent K+ channel (hslo) from human myometrium. Currents were recorded in inside-out macropatches from membranes of Xenopus laevis oocytes. In particular, the inactivation-like process that these channels show at high positive potentials was assessed in order to explore its molecular nature. This current inhibition conferred a bell s...

We compared the characteristics of secretion stimulated by EGTA-buffered Ba(2+)- and Ca(2+)-containing solutions in digitonin-permeabilized bovine adrenal chromaffin cells. Half-maximal secretion occurred at approximately 100 microM Ba2+ or 1 microM Ca2+. Ba(2+)-stimulated release was not due to release of sequestered intracellular Ca2+ because at a constant free Ba2+ concentration, increasing ...

The mechanism ofthe Bat+-induced contraction was investigated using intact and saponin-treated skinned smooth muscle (skinned muscle) strips of the rabbit mesenteric artery . After depletion of Ca21 stored in the caffeinesensitive site, >0 .65 mM Ba2+ evoked contraction in muscle strips depolarized with 128 mM K+ in Cat+-free solution in a dose-dependent fashion, and the ED50 values for Ca2' an...