Renal function and Ca2+ currents after dye-labeling identification of renal sympathetic neurons

The present study was performed to determine whether renal efferent sympath etic neurons could be identified using a retrograde neuronal tracer without compromising renal function and whether the labeling and identification pr ocedure alters Ca2+ currents and neuromodulation of those neurons. Renal sy mpathetic and superior cervical ganglion (SCG) neurons were labeled with th e fluorescent: retrograde tracer fast blue. Renal function studies made 1 w k after labeling revealed that renal hemodynamics and fluid and electrolyte excretion were similar between the dye-injected (left) kidney and the cont rol (right) kidney under control conditions and after hemorrhage. After vol ume expansion, urine flow in the dye-injected kidney was slightly, but sign ificantly, less than that of the control kidney, whereas urinary sodium exc retion increased by approximately ninefold in both kidneys. Patch-clamp stu dies of SCG neurons in 10 mM external Ca2+ revealed that peak currents were not affected by the presence of the dye or a 1-min exposure to ultraviolet (UV) light. Neither maximal norepinephrine-induced Ca2+ current inhibition nor the sensitivity to norepinephrine was affected by the dye or 1-min UV exposure. Facilitation protocols revealed that G protein modulation of Ca2 currents remained intact in dye-labeled UV-exposed neurons. This study dem onstrates that a retrograde fluorescent dye technique to identify renal sym pathetic neurons does not compromise renal function and the presence of the dye label or UV exposure has no effect on Ca2+ currents and neuromodulatio n in these neurons. Isolation of single identified renal sympathetic neuron s coupled with patch-clamp techniques represents a tool to investigate the role of individual current systems in the modulation of excitability in the se neurons, which play an important role in the control of renal hemodynami cs and excretory function and in the pathogenesis of hypertension.