The effects of charybdotoxin (CTX) on single [Ca
2+]
i
-activated potassium channel (
K
(Ca)) activity and whole-cell K
+ currents were examined in rat and mouse pancreatic
-cells in culture using the patch-clamp method. The effects of CTX on glucose-induced electrical activity from both cultured
-cells and
-cells in intact islets were compared. K
(Ca) activity was very infrequent at negative patch potentials (–70
V
m
<0 mv),="" channel="" activity="" appearing="" at="" highly="">
V
m
. K
(Ca) open probability at these depolarized
V
m
values was insensitive to glucose (10 and 20
mm) and the metabolic uncoupler 2,4 dinitrophenol (DNP). However, DNP blocked glucose-evoked action potential firing and reversed glucose-induced inhibition of the activity of K
+ channels of smaller conductance.
The venom from
Leiurus quinquestriatus hebreus (LQV) and highly purified CTX inhibited K
(Ca) channel activity when applied to the outer aspect of the excised membrane patch. CTX (5.8 and 18
nm) inhibited channel activity by 50 and 100%, respectively. Whole-cell outward K
+ currents exhibited an early transient component which was blocked by CTX, and a delayed component which was insensitive to the toxin. The individual spikes evoked by glucose, recorded in the perforated-patch modality, were not affected by CTX (20
nm). Moreover, the frequency of slow oscillations in membrane potential, the frequency of action potentials and the rate of repolarization of the action potentials recorded from pancreatic islet
-cells in the presence of glucose were not affected by CTX.
We conclude that the K(Ca) does not participate in the steady-state glucose-induced electrical activity in rodent pancreatic islets.
Key Words calcium-activated potassium channels - charybdotoxin - pancreatic -cell