Differential expression of BK‐channel isoforms and beta‐subunits in rat neuro‐vascular tissues

The Ca 2+ ‐activated K + channel (BK, MaxiK, Slo, K Ca 1.1) is involved in regulation of smooth muscle tone and shaping of action‐potentials. It appears in several functional forms due to alternative splicing and the presence of modulatory β‐subunits. The expression of these has been suggested to be tissue‐specific, yet the relative abundance in tissues including trigeminal nerve and cerebral blood‐vessels has not been thoroughly determined. By RT‐PCR we investigated the expression of the BK channel splice‐variants and β‐subunits in rat cerebral blood‐vessels, larger arteries, heart, the trigeminal ganglion, brain, inner organs and skeletal muscle. A 58 or 29 aa insert (STREX and e22) was found at splice‐sites two in most vascular tissues and in skeletal muscle respectively, while a 27 aa insert (Slo 27 ) at splice‐site four was found predominantly in brain and trigeminal ganglion. A surprising 92 bp insert was found in Sagital Sinus at a splice‐site (X2), inducing a shift in reading‐frame and truncation of the protein (stop codon). β1 and β4 were found in all tissues except skeletal muscle, and β2 mostly in brain, trigeminal ganglion and cerebral vessels. In conclusion, the Slo 27 insert, β2 and β4 were more abundant in nerve than in vascular tissues (cerebral vessels), while the STREX insert and β1 were less abundant in nerve tissue (trigeminal ganglion), suggesting differential expression of functional BK channel forms.