Low-voltage activated calcium channels are differently affected by nimodipine

Voltage-dependent Ca2+ channels in adult rat sensory neurones were studied as far as their characterization and nimodipine effects are concerned, using patch-clamp whole-cell technique. Low-voltage activated (LVA) Ca2+ currents were identified according to activation and inactivation kinetics and sensitivity to amiloride. Nimodipine (10 nM) caused a decrease in LVA Ca2+ current amplitude (-40% +/- 2.2 s.e.m., n = 11 out of 30 with LVA Ca2+ currents). Conversely, in 6 neurones out of 30 nimodipine increased the Ca2+ current amplitude (+ 10% +/- 2). In some unaffected neurones (n = 5) nimodipine was also tested at higher concentrations (up to 5 microM) without any appreciable effect. In conclusion, nimodipine was partly able to block LVA calcium channels even at nanomolar concentrations. Supposing nimodipine acts directly on the channel, it can be assumed that there may be different types of LVA calcium channels in sensory neurones.