Type I Inositol-Triphosphate Receptor Gene Is Alternatively Spliced in Human Cerebral Arteries

Three distinct genes encode the three isoforms of the inositol triphosphate (IP₃) receptor (type I, II and III) expressed in brain. Coupling domain of neuronal type I receptor contains a 117 nucleotide insert located between two cyclic AMP-dependent protein kinase (PKA) phosphorylation consensus sequences. By contrast, in nonneuronal tissues this insert is removed by alternative splicing. Neuronal tissue and cerebral arteries share the same embryologic origin. The present study was designed to characterize alternative splicing of the type I IP₃ receptor gene in vascular tissue of human brain. Total RNA was isolated from human basilar and middle cerebral arteries and cerebellum. One μg of total RNA was reverse transcribed. First strand cDNA was obtained and used as a template in polymerase chain reaction (PCR). PCR products were subcloned and sequenced. Specific mRNA for type I and II receptors were detected in human cerebral arteries. In vascular tissue, a short transcript was expressed indicating that the type I receptor was alternatively spliced. In contrast, only nonspliced isoform was detected in cerebellum. These results suggest that alternative splicing corresponds to differences in regulation of cerebrovascular and neuronal IP₃ receptors.