Inhibitory actions by ibandronate sodium, a nitrogen-containing bisphosphonate, on calcium-activated potassium channels in Madin–Darby canine kidney cells

Abstract

The nitrogen-containing bisphosphonates used for management of the patients with osteoporosis were reported to influence the function of renal tubular cells. However, how nitrogen-containing bisphosphates exert any effects on ion currents remains controversial. The effects of ibandronate (Iban), a nitrogen-containing bisphosphonate, on ionic channels, including two types of Ca2+-activated K+ (KCa) channels, namely, large-conductance KCa (BKCa) and intermediate-conductance KCa (IKCa) channels, were investigated in Madin–Darby canine kidney (MDCK) cells. In whole-cell current recordings, Iban suppressed the amplitude of voltage-gated K+ current elicited by long ramp pulse. Addition of Iban caused a reduction of BKCa channels accompanied by a right shift in the activation curve of BKCa channels, despite no change in single-channel conductance. Ca2+ sensitivity of these channels was modified in the presence of this compound; however, the magnitude of Iban-mediated decrease in BKCa-channel activity under membrane stretch with different negative pressure remained unchanged. Iban suppressed the probability of BKCa-channel openings linked primarily to a shortening in the slow component of mean open time in these channels. The dissociation constant needed for Iban-mediated suppression of mean open time in MDCK cells was 12.2 μM. Additionally, cell exposure to Iban suppressed the activity of IKCa channels, and DC-EBIO or 9-phenanthrol effectively reversed its suppression. Under current-clamp configuration, Iban depolarized the cells and DC-EBIO or PF573228 reversed its depolarizing effect. Taken together, the inhibitory action of Iban on KCa-channel activity may contribute to the underlying mechanism of pharmacological or toxicological actions of Iban and its structurally similar bisphosphonates on renal tubular cells occurring in vivo.

Characterization of Convergent Suppression by UCL-2077 (3-(Triphenylmethylaminomethyl)pyridine), Known to Inhibit Slow Afterhyperpolarization, of erg-Mediated Potassium Currents and Intermediate-Conductance Calcium-Activated Potassium Channels

“…However, the magnitude of IK Ca -channel openness was clearly subject to reduction by this compound, despite the failure to reduce the unitary amplitude. Moreover, the UCL-2077-mediated decrease in IK Ca -channel activity was notably counteracted by the subsequent application of 9-phenanthrol, an activator of IK Ca channels [35]. Previous observations have shown that the magnitude of IK Ca -channel activity could have significant impacts on the slow afterhyperpolarization of neurons [21,26,27,29].…”

“…No change in the single-channel amplitude of IK Ca channels between the absence and presence of 10 µM UCL-2077 was demonstrated (3.87 ± 0.03 pA (control) versus 3.85 ± 0.03 pA (in the presence of UCL-2077); n = 9, p > 0.05). In the continued presence of UCL-2077 (30 µM), further addition of 9-phenanthrol (10 µM), an activator of IK Ca channels [35], significantly reversed the UCL-2077-mediated suppression of IK Ca channels in these cells ( Figure 7B). Therefore, in addition to its perturbation on the amplitude and gating of I K(erg) , UCL-2077 was capable of diminishing the probability that IK Ca channel would be open.…”

Evidence for Effective Multiple K+-Current Inhibitions by Tolvaptan, a Non-peptide Antagonist of Vasopressin V2 Receptor

“…In another separate set of experiments, we treated GH 3 cells with vasopressin (1 μM) at 37°C for 6 h. The MDCK cell line (BCRC-60004), a canine renal tubular cell line, was also obtained from the Bioresource Collection and Research Center (Hsinchu, Taiwan). MDCK cells were maintained and subcultured in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum (v/v) (Jan et al, 1999; Wu et al, 2015). These cells were maintained at 37°C in a humidified environment of 5% CO 2 /95% air.…”

High Efficacy by GAL-021: A Known Intravenous Peripheral Chemoreceptor Modulator that Suppresses BKCa-Channel Activity and Inhibits IK(M) or Ih

“…Further addition of cilostazol (10 µM), still in the presence of GAL-021 (10 µM), was effective at reversing GAL-021-mediated suppression of BK Ca -channel activity, while that of 9-phenanthrol (10 µM) had minimal effects on it. Cilostazol or 9-phenanthrol have been known to stimulate the activity of BK Ca channels or intermediate-conductance Ca 2+ -activated K + (IK Ca ) channels, respectively [40][41][42]. Therefore, it is apparent that the presence of GAL-021 can decrease the opening probability of BK Ca channels in these cells, but not that of IK Ca channels.…”