Effects of barium on the potassium conductance of squid axon.

Abstract

A B ST R A C T Ba § ion blocks K § conductance at concentrations in the nanomolar range. This blockage is time and voltage dependent. From the time dependence it is possible to determine the forward and reverse rate constants for what appears to be an essentially first-order process of Ba ++ interaction. The voltage dependence of the rate constants and the dissociation constants place the site of interaction near the middle of the membrane field. Comparison of the efficacy of Ba § block at various internal K § concentrations suggests that Ba § is probably a simple competitive inhibitor of K + interaction with the K + conductance. The character of Ba ++ block in high external K + solutions suggests that Ba + § ion may be "knocked-off" the site by inward movement of external K § Examination of the effects of other divalent cations suggests that the channel may have a closed state with a divalent cation inside the channel. The relative blockage at different temperatures implies a strong interaction between Ba + § and the K § conductance.

A calcium‐activated potassium current in motor nerve terminals of the mouse.

“…However, the action of Ba appears to be much more potent from the inside than from the outside (Eaton & Brodwick, 1980). For instance, when we applied 1 mm Ba to mouse motor endings externally, in the absence of K-channel blocking agents, its action was moderate and probably not specific, since it affected the Na and K components of external currents equally.…”

Voltage clamp measurements of the hyperpolarization‐activated inward current I(f) in single cells from rabbit sino‐atrial node.

“…For example, it could produce a significant stimulation of the electrogenic Na+-K+ pump (cf. Gadsby, 1984;Nakao & Gadsby, 1989 (van Bogaert & Carmeliet, 1985) as well as in rabbit S-A node (Seyama, 1979;Yanagihara & Irisawa, 1980 (Eaton & Brodwick. 1980; cf.…”

K+ transport in Malpighian tubules of Tenebrio molitor L.: is a KATP channel involved?

“…In our study, a low bath [K + ] (5 mmol l -1 ), and therefore a high [Na + ] (141 mmol l -1 ), could be responsible for activating the Na + /K + -ATPase, thereby increasing the open probability of the KATP channels. The initial large depolarization seen when changing the bath [K + ] from a low to a high value is most probably due to the following: (1) Ba 2+ , being a competitive inhibitor of K + channels, is 'knocked-off' by the inward flux of K + ions at high bath [K + ] (Eaton and Brodwick, 1980;Armstrong and Taylor, 1980) and (2) the initial intracellular [ATP] is relatively low, which means the open probability of the KATP channels is high, allowing an initial influx of K + ions. However, at a bath concentration containing no NaCl (140 mmol l -1 KCl), the Na + /K + pump stops functioning, resulting in a time-dependent increase of intracellular [ATP] and therefore the closing of KATP channels.…”