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Beta cells, potassium channels, and insulin
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    It seems that the term, nesidioblastosis, is out and persistent hyperinsulinaemic hypoglycaemia of infancy (PHHI) is in. In familial PHHI mutations have been found in the gene on the short arm of chromosome 11 which codes for a β cell potassium channel protein, the sulfonylurea receptor. Now work in Sheffield, Leicester, and London (Charlotte Kane and colleagues, Nature Medicine 1996;2:1344-7) has shown a potassium channel defect in non-familial PHHI.

     The β cells from partial pancreatectomy specimens from five infants were studied in culture and electrophysiological recordings demonstrated the absence of ATP-sensitive potassium (KATP) channel activity in all five. In normal β cells glucose entry produces more ATP which closes KATP channels. The resultant membrane depolarisation opens calcium channels and an influx of calcium brings about insulin release. Increased intracellular calcium was demonstrated in the PHHI β cells from these five infants.

     It appears, therefore, that PHHI is caused by a lack of KATP activity which results in spontaneous electrical activity and insulin release. In an article in this journal in 1996 (74:373-8) the same workers reported a favourable response to calcium channel blockade in an infant with PHHI.

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