PA1b, a plant peptide, induces intracellular [Ca^(2+)] in- crease via Ca^(2+) influx through the L-type Ca^(2+) channel and triggers secretion in pancreatic β cells

Using alginic acid to adsorb polypeptides at pH 2.7, we isolated a peptide pea albumin 1b (PA1b) from pea seeds. The PA1b is a single chain peptide consisting of 37 amino acid residues with 6 cysteines which constitutes the cystine-knot structure. Using microfluorometry and patch clamp techniques, we found that PA1b significantly elevated the intracellular calcium level ([Ca2+ ]i) and elicited membrane capacitance increase in the primary rat pancreatic β cells. The PA1b effect on [Ca2+]i elevation was abolished in the absence of extracellular Ca2+ or in the presence of L-type Ca2+ channel blocker, ni- modipine. Interestingly, we found that PA1b significantly depolarized membrane potential, which could lead to the opening of voltage-dependent L-type Ca2+ channels and influx of extracellular Ca2+, and then evoke robust secretion. In this study we identified the plant peptide PA1b which is capable of affecting the excitability and function of mammalian pancreatic β cell.