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Specific inhibition of long-lasting, L-type calcium channels by synthetic parathyroid hormone
Abstract:
The effect of an active synthetic N-terminal fragment of bovine parathyroid hormone (bPTH), bPTH-(1-34), on Ca2+ channels was studied in mouse neuroblastoma cells (N1E-115). With the whole-cell variation of the patch-clamp technique, T (transient) and L (long-lasting) types of Ca2+ currents were identified. Pharmacological characterization showed that the L current was amplified by the Ca2+ channel stimulator BAY K-8644, but the T current was unaffected. The administration of bPTH-(1-34) produced dose-related inhibition of the L current, which could be reversed by BAY K-8644. The peptide had no effect on the T current. In addition, use of the fluorescent indicator fura-2 showed that bPTH-(1-34) inhibited the KCl-stimulated increase in intracellular free Ca2+ in neuroblastoma cells with L channels but not in cells with T channels. An inactivated (oxidized) preparation of bPTH-(1-34) failed to affect the L current. High-affinity binding of labeled PTH analog to these neuroblastoma cells was also demonstrated. In addition, bPTH-(1-34) inhibited the L current in cultured vascular smooth muscle cells from rat tail artery. These data indicate that, in some tissues, PTH can act as an endogenous blocker of Ca2+ entry.
Insights
Bovine parathyroid hormone (bPTH)-(1-34) inhibits L-type calcium channels in neuroblastoma and smooth muscle cells. This peptide acts as an endogenous calcium channel blocker, affecting intracellular calcium levels.
Area of Science:
- Neuroscience
- Pharmacology
- Cell Biology
Background:
- Parathyroid hormone (PTH) plays a crucial role in calcium homeostasis.
- The specific effects of PTH on ion channels, particularly calcium channels, are not fully elucidated.
- Understanding PTH's interaction with calcium channels is vital for various physiological and pathological processes.
Purpose of the Study:
- To investigate the effect of bovine parathyroid hormone (bPTH)-(1-34) on calcium (Ca2+) channels in mouse neuroblastoma cells.
- To determine whether bPTH-(1-34) modulates T-type and L-type Ca2+ currents.
- To explore the potential role of PTH as an endogenous modulator of Ca2+ entry in different cell types.
Main Methods:
- Utilized the whole-cell patch-clamp technique to identify and characterize T-type and L-type Ca2+ currents.
- Employed pharmacological agents like BAY K-8644 to modulate Ca2+ channel activity.
- Used the fluorescent indicator fura-2 to measure intracellular free Ca2+ concentrations.
- Tested inactivated bPTH-(1-34) and performed binding assays with labeled PTH analogs.
- Examined the effects on cultured vascular smooth muscle cells.
Main Results:
- bPTH-(1-34) dose-dependently inhibited L-type Ca2+ currents, an effect reversible by BAY K-8644.
- T-type Ca2+ currents were unaffected by bPTH-(1-34).
- bPTH-(1-34) reduced KCl-stimulated intracellular Ca2+ increase in cells with L channels but not T channels.
- Active bPTH-(1-34) demonstrated high-affinity binding to neuroblastoma cells.
- Inhibition of L-type Ca2+ current was also observed in rat vascular smooth muscle cells.
Conclusions:
- bPTH-(1-34) acts as a specific blocker of L-type calcium channels.
- PTH may function as an endogenous inhibitor of Ca2+ entry in certain cell types, including vascular smooth muscle.
- These findings suggest a novel role for PTH in regulating cellular calcium dynamics beyond its classical endocrine functions.