Effects of divalent cations and La³⁺ on contractility and ecto‐ATPase activity in the guinea‐pig urinary bladder

1

Several cations (Ba²⁺, Cd²⁺, Co²⁺, Cu²⁺, Mn²⁺, Ni²⁺, Zn²⁺ and La³⁺, all as chloride salts, 1–1000 μm) were tested in the guinea‐pig urinary bladder for their ability to: (i) modify contractile responses to electrical field stimulation (EFS), ATP, α,β‐methylene ATP (α,β‐meATP), carbachol (CCh), and KCl; (ii) affect ecto‐ATPase activity.

Several cations (Ba²⁺, Cd²⁺, Co²⁺, Cu²⁺, Mn²⁺, Ni²⁺, Zn²⁺ and La³⁺, all as chloride salts, 1–1000 μm) were tested in the guinea‐pig urinary bladder for their ability to: (i) modify contractile responses to electrical field stimulation (EFS), ATP, α,β‐methylene ATP (α,β‐meATP), carbachol (CCh), and KCl; (ii) affect ecto‐ATPase activity.

Ba²⁺ (10–1000 μm) concentration‐dependently potentiated contractile responses evoked by EFS (4–16 Hz), ATP (100 μm), α,β‐meATP (1 μm), CCh (0.5 μm), and KCl (30 mm). Ni²⁺ at concentrations of 1–100 μm also potentiated contractility of the urinary bladder, but at concentrations tested its effect was not concentration‐dependent. Cu²⁺ at a concentration of 10 μm and Cd²⁺ at a concentration of 1 μm potentiated responses to all stimuli, except KCl. Ni²⁺ at a concentration of 1000 μm and Cd²⁺ at a concentration of 100 μm inhibited contractions evoked by all stimuli, and at a concentration of 1000 μm Cd²⁺ abolished any contractions. Responses to ATP and α,β‐meATP were selectively inhibited by Cu²⁺, Zn²⁺ or La³⁺, each at a concentration of 1 mm.

Cu²⁺, Ni²⁺, Zn²⁺ and La³⁺ (100–1000 μm) concentration‐dependently inhibited ecto‐ATPase activity in the urinary bladder smooth muscle preparations, while Ba²⁺ and Mn²⁺ were without effect, and Cd²⁺ and Co²⁺ caused significant inhibition only at a concentration of 1000 μm.

There was no correlation between the extent of ecto‐ATPase inhibition and the effect on contractile activity of any of the cations.

In conclusion, the ability of some divalent cations to inhibit ecto‐ATPase activity and to potentiate or inhibit contractile responses in the guinea‐pig urinary bladder appear to be independent effects.

DOI: 10.1111/j.1476-5381.1995.tb17186.x

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