Rae, James L.

The effects of melatonin on ionic conductances in a cultured mouse lens epithelial cell line (α-TN4) and in cultured human trabecular meshwork (HTM) cells were measured using the amphotericin perforated patch whole cell voltage-clamp technique. Melatonin stimulated a voltage-dependent Na+-selective current in lens epithelial cells and trabecular meshwork cells. The effects of melatonin were observed at 50 pM and were maximal at 100 μM. Melatonin enhanced activation and inactivation kinetics, but no change was observed in the voltage dependence of activation. The results are consistent with an increase in the total number of ion channels available for activation by membrane depolarization. Melatonin was also found to stimulate a K+-selective current at high doses (1 mM). Melatonin did not affect the inwardly rectifying K+ current or the delayed rectifier type K+ current that has been described in cultured mouse lens epithelial cells. The results show that melatonin specifically stimulated the TTX-insensitive voltage-dependent Na+ current by an apparently novel mechanism.

The five string banjo is a stringed instrument that uses a drum head (membrane) to radiate sound. The strings couple to the head through a moveable bridge. Many have a removable resonator whose spacing from the main part of the banjo is adjustable to allow tuning of the internal air cavity. Holographic interferometry demonstrates vibrational modes of the head that have a strong dependence on head tension. Driving point accelerance measurements demonstrate that the ability of the bridge to be vibrated depends on the mass and stiffness of the materials used in its construction. Peak accelerances usually occur between 1800–2000 Hz. Power spectra measurements of the sound show that 99% of the sound is in a frequency range of 147–5200 Hz. Two substantial formants are seen in the power spectra. The first and largest occurs in about the 400–1800 Hz range, the same frequency range where the most substantial head modes are found. The second is from 2000–4000 Hz, a range where the series combination of bridge and head show increasing accelerances by driving point measurements. Measurements of the transient response following a pluck quantify the frequency content of the rising and falling phase.

Smooth muscle exhibits mechanosensitivity independent of neural input, suggesting that mechanosensitive pathways reside within smooth muscle cells. The native L-type calcium current recorded from human intestinal smooth muscle is modulated by stretch. To define mechanosensitive mechanisms involved in the regulation of smooth muscle calcium entry, we cloned the α1C L-type calcium channel subunit (CaV1.2) from human intestinal smooth muscle and expressed the channel in a heterologous system. This channel subunit retained mechanosensitivity when expressed alone or coexpressed with a β2 calcium channel subunit in HEK-293 or Chinese hamster ovary cells. The heterologously expressed human cardiac α1C splice form also demonstrated mechanosensitivity. Inhibition of kinase signaling did not affect mechanosensitivity of the native channel. Truncation of the α1C COOH terminus, which contains an inhibitory domain and a proline-rich domain thought to mediate mechanosensitive signaling from integrins, did not disrupt mechanosensitivity of the expressed channel. These data demonstrate mechanical regulation of calcium entry through molecularly identified L-type calcium channels in mammalian cells and suggest that the mechanosensitivity resides within the pore forming α1C-subunit.