Intracellular calcium concentration in the inositol trisphosphate receptor type 1 knockout mouse

Recently, mice with a disrupted inositol trisphosphate (IP3) receptor type 1 allele were produced by gene targeting. To examine the role of IP3 receptor type 1 in the regulation of intracellular calcium concentration ([Ca²⁺](i)) of glomerular cells, [Ca²⁺](i) was measured with fura 2- acetoxymethyl-ester in the superfused glomeruli from homozygous and wild-type mice. [Ca²⁺](i) was determined in calcium-free medium before and after the addition of 10^-7 M endothelin-1 (ET- 1) and 10^-6 M angiotensin II (AngII). The expression of mRNA of IP3 receptor isoforms and hormone receptors in the glomeruli from these animals also was measured by quantitative reverse transcription-PCR with specific primers for IP3 receptor isoforms (types 1, 2, and 3), AngII receptor type 1, and ET receptors (types A and B). In homozygous mutants, the shorter mRNA of IP3 receptor type 1, which lacks the first exon, is transcribed. Basal [Ca²⁺](i) and the responses to ET-1 and AngII in homozygous mutants (ET-1, 55 ± 7 nM to 73 ± 7 nM; AngII, 66 ± 6 to 91 ± 8 nM) were significantly lower than those in the wild-type mice (ET-1, 93 ± 13 nM to 162 ± 13 nM; AngII, 87 ± 7 to 147 ± 9 nM; P < 0.05 for both hormones) without significant changes in mRNA expression of hormone receptors. The results with quantitative reverse transcription-PCR also revealed that mRNA expression of the IP3 receptor gene family was not significantly different between the two groups. The present study clearly shows that IP3 receptor type 1 plays a major role in the regulation of [Ca²⁺](i) in the glomeruli and that lack of an isoform of IP3 receptor in the glomeruli does not induce expression of the other isoforms of the IP3 receptor.