Effects of serotonin on electrical properties of Madin-Darby canine kidney cells

The present study has been performed to test for the influence of serotonin on the potential difference across the cell membrane (PD) of Madin-Darby canine kidney (MDCK)-cells. Under control conditions PD averages -48.6±0.6 mV (n=98). Increasing extracellular potassium concentration from 5.4 to 10 and 20 mmol/l depolarizes the cell membrane by +6.3±0.6 mV (n=6) and +14.1±1.0 mV (n=12), respectively. The cell membrane is transiently hyperpolarized to -67.8±0.8 mV (n=63) by 1 µmol/l serotonin. In the presence of serotonin, increasing extracellular potassium concentration from 5.4 to 20 mmol/l depolarizes the cell membrane by +26.4±1.0 mV (n=11). 1 mmol/l barium depolarizes the cell membrane by +15.7±1.3 mV (n=17) and abolishes the effect of step increases of extracellular potassium concentration from 5.4 to 10 mmol/l. In the presence of barium, serotonin leads to a transient hyperpolarization by -26.3±1.0 mV (n=16). During this transient hyperpolarization, the cell membrane is sensitive to extracellular potassium concentration despite the continued presence of barium. 10 µmol/l methysergide hyperpolarize the cell membrane by -7.2±2.0 mV (n=6). In the presence of 10µmol/l methysergide, the effect of serotonin is virtually abolished (+0.4±0.9 mV,n=6). 1 µmol/l ketanserin, a 5-HT₂ receptor blocking agent, ICS 205-930, a 5-HT₃ receptor blocking agent, and phentolamine, an unspecific a-receptor blocking agent, do not significantly modify the effect of serotonin. In the nominal absence of extracellular calcium, the effect of serotonin is markedly reduced. In conclusion, serotonin hyperpolarizes MDCK-cells by increasing apparent potassium conductance. This effect is transmitted by 5-HT₁ receptors and depends on extracellular calcium.