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

We investigated the expression of splice variants and beta-subunits of the BK channel (big conductance Ca2+-activated K+ channel, Slo1, MaxiK, KCa1.1) in rat cerebral blood vessels, meninges, trigeminal ganglion among other tissues. An alpha-subunit splice variant X1(+24) was found expressed (RT-PCR) in nervous tissue only where also the SS4(+81) variant was dominating with little expression of the short form SS4(0). SS4(+81) was present in some cerebral vessels too. The SS2(+174) variant (STREX) was found in both blood vessels and in nervous tissue. In situ hybridization data supported the finding of SS4(+81) and SS2(+174) in vascular smooth muscle and trigeminal ganglion. beta-subunits beta2 and beta4 showed high expression in brain and trigeminal ganglion and some in cerebral vessels while beta1 showed highest expression in blood vessels. beta3 was found only in testis and possibly brain. A novel splice variant X2(+92) was found, which generates a stop codon in the intracellular C-terminal part of the protein. This variant appears non-functional as a homomer but may modulate the function of other splice-variants when expressed in Xenopus oocytes. In conclusion a great number of splice variant and beta-subunit combinations likely exist, being differentially expressed among nervous and vascular tissues.