Pathophysiological stimuli, including hypoxia, lead to K⁺ efflux from the intracellular lumen to the extracellular space, thereby increasing local tissue K⁺ concentrations and depolarizing resident cells. In this study, we investigated the effects of increased extracellular K⁺ concentrations ([K⁺]_e) on heat shock protein (HSP) expression in the porcine proximal tubule epithelial cell line LLC-PK₁. We analyzed HSP-25, HSP-72, HSC-73, and HSP-90 protein expression by Western blot analyses and HSP-72 promoter activity by luciferase reporter gene assays using the proximal 1,440 bp of the HSP-72 promoter. Elevating [K⁺]_e from 20 to 50 mM increased HSP-72 protein expression and promoter activity but did not affect HSP-25, HSC-73, or HSP-90 levels. Addition of identical concentrations of sodium chloride did not increase HSP-72 expression to a similar amount. The Ca²⁺ channel blocker diltiazem and the Ca²⁺-specific chelator EGTA-AM abolished high [K⁺]_e-induced HSP-72 expression by 69.7 and 75.2%, respectively, indicating that the transcriptional induction of HSP-72 involves Ca²⁺ influx. As measured by confocal microscopy using the Ca²⁺ dye fluo 3-AM, we also observed a rapid increase of intracellular Ca²⁺ concentration as early as 30 s after placing LLC-PK₁ cells in high [K⁺]_e. We further analyzed whether Ca²⁺ influx was necessary for induction of HSP-72 expression by high [K⁺]_e using Ca²⁺-free medium. Here, induction of HSP-72 in response to high [K⁺]_e was completely abolished. Our data thus demonstrate activation of a protective cellular response to ionic stress, e.g., elevated K⁺ concentrations, by specifically increasing protein levels of HSP-72.