Background—We recently demonstrated that phospholipase C (PLC)--1 activity in cultured skin fibroblasts obtained from patients with coronary spastic angina (CSA) is enhanced. We tested the hypothesis that structural abnormality in PLC-1 isoform is a cause of the enhanced activity.

Methods and Results—Sequence analysis of the cDNA coding for PLC-1 obtained from fibroblasts revealed that one conversion of guanine to adenine (A) was present at nucleotide position 864 in one CSA patient, resulting in the amino acid replacement of arginine 257 by histidine (R257H). The incidence of 864A/A in genomic DNA, analyzed by single-strand conformation polymorphism, was greater in patients with CSA than in male control subjects (6 of 57 patients with CSA versus 1 of 62 control subjects, P<0.05). The activity of the variant PLC-1 protein under free calcium concentration between 10^-8 and 10^-7 mol/L was 2-fold higher than that of the wild-type protein. Baseline intracellular calcium concentration ([Ca²⁺]_i) in human embryonic kidney 293 cells transfected with the variant PLC-1 was higher than that in cells with the wild type. The peak increase in [Ca²⁺]_i in response to acetylcholine at 10^-6 and 10^-5 mol/L was greater in the cells with the variant PLC-1 than in those with the wild type.

Conclusions—These findings indicate that the R257H variant in the PLC-1 gene detected in patients with CSA is associated with enhancement of enzyme activity, and they describe a novel mechanism for the enhanced coronary vasomotility in CSA.