Dopamine-induced epithelial K+ and Na+ movements in the salivary ducts of Periplaneta americana

K+- and Na+-selective double-barrelled microelectrodes were used for intracellular and luminal measurements in salivary ducts of Periplaneta americana. The salivary ducts were stimulated with dopamine (10−6 mol l−1). Dopamine decreased intracellular [K+] from 112±17 mmol l−1 to 40±13 mmol l−1 (n=6) and increased intracellular [Na+] from 22±19 mmol l−1 to 92±4 mmol l−1 (n=6). Luminal [K+] was 15±3 mmol l−1 in the unstimulated salivary ducts and increased to 26±11 mmol l−1 upon stimulation with dopamine (n=10). Luminal [Na+] was insignificantly increased from 105±25 mmol l−1 to 116±22 mmol l−1 (n=12) by stimulation with dopamine. The potential difference across the basolateral membrane (PDb) was depolarized from −65±6 mV to −31±13 mV (n=12) and the transepithelial potential difference (PDt) was hyperpolarized from −13±6 mV to −22±7 mV (n=22, lumen negative) upon stimulation with dopamine. The re-establishment of prestimulus values of intracellular [K+] and [Na+] and PDb was inhibited by basolateral addition of ouabain (10−4 mol l−1). Furosemide (10−4 mol l−1) in the bath inhibited the dopamine-induced increase in intracellular [Na+], the decrease in intracellular [K+] and the depolarization of PDb. We propose a model for dopamine-stimulated ion transport in the salivary ducts involving basolateral Na+-K+-2Cl− cotransport and active extrusion of K+ via the apical membrane.