The effects of neuroleptic and tricyclic compounds on BK_Ca channel activity in rat isolated cortical neurones

Abstract

1. The actions of several neuroleptic and tricyclic compounds were examined on the large conductance Ca²⁺-activated K⁺ (BK_Ca) channel present in neurones isolated from the rat motor cortex.

2. Classical neuroleptic compounds including chlorpromazine and haloperidol applied to the intracellular surface of inside-out patches produced a concentration-dependent reduction in BK_Ca channel activity. Similar effects were observed when these compounds were applied to the extracellular surface of outside-out patches.

3. In contrast, the atypical neuroleptic compounds clozapine and sulpiride did not affect BK_Ca channel activity (100 nM–1 mM) in either inside-out or outside-out patches, while 10 μM pimozide produced 73% of the inhibition produced by 10 μM chlorpromazine.

4. BK_Ca channel activity was also unaffected by application of structurally related tricyclic compounds including the anti-cholinesterase tacrine and the anti-epileptic carbamazepine. The tricyclic antidepressant drug amitriptyline was found to inhibit BK_Ca channel activity but was much less effective than the classical neuroleptic compounds.

5. It is concluded that compounds belonging to the classical neuroleptic group of drugs inhibit BK_Ca channel activity in the rat motor cortex in a structurally-specific manner. This observation may be of clinical significance as it may contribute to some of the side effects associated with classical neuroleptic drug therapy.

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