Differential expression of the α and β subunits of the large-conductance calcium-activated potassium channel: implication for channel diversity
Abstract In addition to the large α subunits that conduct selective ion currents, many native voltage-gated ion channels contain associated proteins which modulate the channel activity. Recently, a β subunit of the large-conductance calcium-activated K + (BK) channel has been cloned and functionally characterized. In this report, we studied the tissue distribution of the α and β subunits of rat BK channels by nuclease protection analyses and in situ hybridization. BK α mRNA is widely distributed but is especially enriched in the brain. In the adult brain, BK α expression is robust and widespread throughout all areas of the neo-, olfactory and hippocampal cortices, habenula and cerebellum. Other prominent sites of BK α expression include thalamus and amygdala. In marked contrast to the expression pattern of BK α mRNA, the expression of BK β mRNA is relatively low and preferentially in the periphery. In rat brains, BK β mRNA occurs only in a few discrete populations of neurons that also express BK α messages. These results indicate that the major type of BK channels in the brain, unlike the αβ channel type in aortic and tracheal smooth muscle, is devoid of the β subunit. These observations provide a structural basis for the BK channel diversity observed in a variety of tissues.