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Parasympathetic stimulation of the heart, which provides protection from arrhythmias and sudden death, involves activation of the G protein--coupled inward rectifying [K.sup.+] channel GIRK1/4 and results in an acetylcholine-sensitive [K.sup.+] current, [I.sub.KACh]. We describe a unique relationship between lipid homeostasis, the lipid-sensitive transcription factor SREBP-1, regulation of the cardiac parasympathetic response, and the development of ventricular arrhythmia. In embryonic chick atrial myocytes, lipid lowering by culture in lipoprotein-depleted serum increased SREBP-1 levels, GIRK1 expression, and [I.sub.KACh] activation. Regulation of the GIRK1 promoter by SREBP-1 and lipid lowering was dependent on interaction with 2 tandem sterol response elements and an upstream E-box motif. Expression of dominant negative SREBP-1 (DN--SREBP-1) reversed the effect of lipid lowering on [I.sub.KACh] and GIRK1. In SREBP-1 knockout mice, both the response of the heart to parasympathetic stimulation and the expression of GIRK1 were reduced compared with WT. [I.sub.KACh], attenuated in atrial myocytes from SREBP-1 knockout mice, was stimulated by SREBP-1 expression. Following myocardial infarction, SREBP-1 knockout mice were twice as likely as WT mice to develop ventricular tachycardia in response to programmed ventricular stimulation. These results demonstrate a relationship between lipid metabolism and parasympathetic response that may play a role in arrhythmogenesis., Introduction The balance between the response of the heart to sympathetic and parasympathetic stimuli not only determines the rate and force of contraction but also plays a role in regulating [...]