Cromakalim: embryonic effects and reduction of tolbutamide-induced dysmorphogenesis in vitro

Cromakalim is a K(+) channel opener that causes smooth muscle relaxation by activating ATP-sensitive K(+) (K(ATP)) channels and producing membrane hyperpolarization. Cromakalim counteracts sulfonylurea-induced K(ATP) channel inhibition in adult cells, but little is known regarding its embryonic effects, alone or in combination with sulfonylureas. K(ATP) channels have been demonstrated in the embryo, but their role in normal and abnormal development is unknown. Early-somite mouse embryos were exposed for 24 hr in vitro to cromakalim at concentrations of 0 (Cntl), 1, 10, 100, 200, or 500 microM in 0.125% DMSO. Embryos were also exposed for 24 hr in vitro to a dysmorphogenic tolbutamide concentration (110 microg/ml) combined with a subdysmorphogenic concentration of cromakalim (1 microM). Embryos were evaluated for somite number, heart rate, malformations, and embryonic and yolk sac protein content. Embryos exposed to 1 microM cromakalim were similar to controls. Cromakalim exposure increased malformation rates at concentrations >/=200 microM, decreased heart rates at >/=10 microM, and decreased somite and protein values at 500 microM. Defects involved cranial neural tube, optic vesicle, heart, and somites. A malformation rate of 59% in embryos exposed to 110 microg/ml tolbutamide was reduced to 13% by adding 1 microM cromakalim to the culture medium. Heart rate, somite number, and protein values were also improved by combined exposure to cromakalim and tolbutamide compared with exposure to tolbutamide alone. These results support previous findings with diazoxide (K(+) channel opener) and chlorpropamide (sulfonylurea) and further suggest a potential role for K(ATP) channel effects in sulfonylurea-induced dysmorphogenesis.