Differential effects of dopamine on a potassium current in cultured Rutabaga and wild-type Drosophila cells

The rutabaga mutation which has a low intracellular cyclic adenosine monophosphate (cAMP) concentration is defective in short-term memory. The aim of this study was to compare modulation effects of dopamine on the delayed-rectifier potassium current (IKDR) in rutabaga and wild-type Drosophila neurons. The conventional whole-cell patch-clamp technique was applied to cultured Drosophila neurons derived from embryonic neuroblasts. IKDR was measured from cultured (2 days) wild-type and rutabaga neurons. IKDR was smaller in rutabaga neurons (373 +/- 38 pA) than in wild-type neurons (519 +/- 40 pA) but there was no difference in IKDR activation or inactivation between the two genotypes. We examined the effects of dopamine on IKDR in wildtype and rutabaga neurons. IKDR was measured from neurons before and after addition of dopamine to the external solution. Dopamine application reduced IKDR in wild-type neurons but did not significantly affect IKDR in rutabaga neurons (single-cell studies). In the presence of dopamine there was no difference in IKDR between wild-type (344 +/- 29 pA) and rutabaga (338 +/- 27 pA) neurons (population studies). These results indicate that dopamine differentially affects the delayed-rectifier channel in wild-type and rutabaga neurons. This can alter neuronal excitability in rutabaga and may affect the processing of neural signals necesssary for learning and memory.